ppc64el installs not preseeded via grub

[Mathieu Trudel-Lapierre]

Starting a ppc64el install in a VM yields an install that isn't preseeded, and only includes the standard task:

 | linux /install/vmlinux tasks=standard pkgsel/language-pack-p\|
 |atterns= pkgsel/install-language-support=false --- quiet |
 | initrd /install/initrd.gz

This appears to be because on ppc64el, we only configure yaboot -- systems booting the CD with grub (such as ppc64el qemu VMs, but probably hardware too) get a system that doesn't include the usualy ubuntu-server seed: not disabling splash and quiet, forcing the server task, etc.

The ubuntu-server*.seed files are included on the CD but not pointed at by grub because we simply copy the data from d-i without any modification, whereas for amd64, the grub config is modified.